As an exhaust gas purification device arranged in an exhaust passage of an internal combustion engine, there has been known one which receives therein an NSR catalyst. As a method for diagnosing an abnormality in the exhaust gas purification device receiving the NSR catalyst, there has been known one in which an amount of NOx occluded or stored in the NSR catalyst (hereinafter, referred to as a storage amount of NOx) is obtained at the time when an amount of NOx flowing out from the NSR catalyst exceeded a fixed amount, and the abnormality of the exhaust gas purification device is diagnosed based on the storage amount of NOx.
Specifically, in a construction in which an NOx sensor capable of measuring a concentration of NOx in an exhaust gas is arranged in the exhaust passage at the downstream side of the exhaust gas purification device, an amount of NOx, which has been stored in the NSR catalyst in a period of time from a time point at which processing for regenerating the NOx occlusion or storage capacity of the NSR catalyst ended until a time point at which the output of the NOx sensor exceeds a fixed value, is calculated, and when the thus calculated value is smaller than a threshold value, a diagnosis is made that the exhaust gas purification device is abnormal (for example, see a first patent literature).